Adaptive performance-guaranteed control of UPS systems

Uninterruptible Power Supply (UPS) is widely utilized to provide stable and high quality electricity for varying loads. Moreover, it is a critical means to maintain the voltage level of a microgrid with low-inertia. The control performance of UPS system directly affects the reliability and electricity quality of a microgrid. A large voltage deviation could result in component failure or even grid shutdown. In this paper, an adaptive performance-guaranteed controller is proposed for UPS integrated microgrid suffering from unknown parameters and nonlinear loads. A constrained state-space model of the plant is firstly developed and transformed into an equivalent unconstrained one via an error transformation technique. An adaptive controller is subsequently designed for the transformed system by using backstepping scheme. By this means, the bus voltage can be guaranteed to stay within arbitrarily user-defined bounds. Furthermore, all signals within the closed-loop system are proved to be bounded thru Lyapunov synthesis. Finally, the feasibility of the theoretical results is demonstrated via extensive simulation and experimental studies.